1. Field of the Invention
This invention relates to a data recording method suitable for use in an erasable optical disc, especially an optical disc having compatibility with a CD format.
2. Description of the Prior Art
A CD (compact disc) using, for example, a magneto-optical disc as a recording medium and capable of recording and reproducing data has been proposed. Such a CD capable of recording and reproducing data is hereafter called called a CD-RAM. One of characteristics of a CD-RAM is compatibility of data with a CD-ROM which is only for use in playback of data or a CD-WO of a write once type.
In a CD-RAM, one subcode block in the CD format corresponds to one sector. One subcode block consists of 98 frames. Each sector is dealt with as a unit for recording and playback of data.
Note that an error correction code in an ordinary CD is not completed in one sector. Recording and playback of data on a sector-unit basis are therefore difficult. From this viewpoint, the inventor of the present application formerly proposed CIRC (cross interleave Reed Solomon code) of a sector completion type as disclosed in the specification of Japanese Patent Laid Open Publication No. Hei 1-287872 as being an error correction coding method by which data can be recorded and reproduced on the sector-unit basis.
There has been a proposal to perform tracking control by using a sample servo system in case that a magneto-optical disc is used as a recording medium. The sample servo system is known as using servo areas provided at intervals of a predetermined length which is obtained by dividing one sector into a plurality of segments (for example, in each segment), and using a playback signal of each servo area for tracking control.
In order to maintain a stable servo in the sample servo system, it is necessary to determine the interval between servo areas and the length of the servo area according to the rotation speed of a disc and the servo characteristics.
If, however, the interval between servo areas and the length of the servo area are simply determined, merely considering maintenance of a stable servo, error correction processing would be difficult when some defect occurs in servo areas. More specifically, when a defect occurs in a servo area, the level of a playback RF signal drops, and the data of the segment would become an error. If data of one segment extends over a plurality of error correction coding series, it is difficult to process such error in the data of one segment. This is explained in, for example, U.S. Pat. No. 4,907,215.
If maintenance of a stable servo alone is considered to determine the interval between servo areas and the length of the servo area, it would be difficult to establish compatibility of data with other CD variation discs such as CD-ROM, CD-WO, and so on.
In a CD-RAM, it is necessary to provide a sector address in order for data to be recorded in and reproduced from any desired sector. In an ordinary optical disc, a header area is provided, for example, in the leading segment in one sector so that the sector address is recorded in the header area. It is therefore considered that, also for a CD-RAM, the sector address may be recorded, for example, in the leading segment of one sector.
In a CD-RAM, however, one subcode block corresponds to one sector (98 frames) for maintaining compatibility of data. Therefore, the sector size is larger than an ordinary optical disc. In this case with a large sector size, if the sector address is recorded, for example, in the leading one segment alone of one sector, the latency time until the segment with the sector address recorded is reproduced is long, which causes an increase of the access time for reaching the desired sector.